Process for the preparation of cyclopropyldiketopiperazines and of a key intermediate of ds-5272

ABSTRACT

Object of the present invention is an improved process for the preparation of cyclopropyldiketopiperazines and thereof key intermediates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/481,628, filed Jul. 29, 2019 which in turn is a 371 ofPCT/EP2018/050838, filed Jan. 15, 2018, which claims the benefit ofEuropean Patent Application No. 17155811.7, filed Feb. 13, 2017, thecontents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention refers to process for the preparation ofcyclopropyldiketopiperazines, which also are key intermediates for thesynthesis of compound having anti-tumor activity, in particular of thecompound named DS-5272.

BACKGROUND ART

The present invention relates to a convenient process for thepreparation of cyclopropyldiketopiperazines, one of them being a keyintermediate for the synthesis of a potent and orally active p53-MDMSinteraction inhibitor. In particular, for example, the compound namedDS-5272 or((5R,6S)-5-(4-chloro-3-fluorophenyl)-6-(6-chloropyridin-3-yl)-3-isopropyl-6-methyl-5,6-dihydroimidazo[2,1-b]thiazol-2-yl)((2S,4R)-2-((R)-6-ethyl-4,7-diazaspiro[2.5]octane-7-carbonyl)-4-fluoropyrrolidin-1-yl)methanone,having the following structure:

is an active pharmaceutical ingredient which acts as a potent inhibitorof p53-MDM2, therefore, useful to treat cancer.

The patent publication EP2380892A, discloses a class of MDM2 inhibitor,which are potent inhibitors of p53-MDM2 therefore useful for thetreatment of human cancer. In particular the selected active compound((5R,6S)-5-(4-chloro-3-fluorophenyl)-6-(6-chloropyridin-3-yl)-3-isopropyl-6-methyl-5,6-dihydroimidazo[2,1-b]thiazol-2-yl)((2S,4R)-2-((R)-6-ethyl-4,7-diazaspiro[2.5]octane-7-carbonyl)-4-fluoropyrrolidin-1-yl)methanone is prepared,in example 5, by coupling of the intermediate 1 named(5R,6S)-5-(4-chloro-3-fluorophenyl)-6-(6-chloropyridin-3-yl)-6-methyl-3-(propan-2-yl)-5,6-dihydro-imidazo[2,1-b][1,3]thiazole-2-carboxylicacid and having the following structure:

with the Intermediate 2 named1-{(6R)-6-ethyl-7-[(2S,4R)-4-fluoropyrrolidine-2-carbonyl]-4,7-diazaspiro[2.5]octan-4-yl}-2,2,2-trifluoroethan-1-oneand having structure:

followed by the removal of the COCF₃ protecting group.

The preparation of the Intermediate 2 is also disclosed in details inthe example 10 and 11 of the same patent publication, as a syntheticmethod involving six steps of synthesis, starting from methyl(2R)-2-(benzylamino)butanoate, according to the following schema:

According to said publication, the key Intermediate 3, named(6R)-7-benzyl-6-ethyl-4,7-diazaspiro[2.5]octane-5,8-dione and having thefollowing structure:

is prepared in two steps from the compound named methyl(2R)-2-(benzylamino)butanoate, and having the following structure:

The same procedure is disclosed in another patent publication, i.e.EP2336132A, wherein it is disclosed the synthesis of the compound named7-benzyl-4,7-diazaspiro[2.5]octane-5,8-dione of formula:

Said prior art methods for the preparation of(6R)-7-benzyl-6-ethyl-4,7-diazaspiro[2.5]octane-5,8-dione of formula:

require many synthetic steps, the use of starting materials quiteexpensive such as1-{[(benzyloxy)carbonyl]amino}cyclopropane-1-carboxylic acid or methyl(2R)-2-anilinobutanoate, or their preparation.

Moreover, said prior art methods require the use of hydrogen atmospheresfor carried out the cyclisation reaction of step 2, i.e. reductionreaction. The use of hydrogen atmospheres required particular reactorscapable of withstanding high pressure, i.e. autoclaves.

Furthermore, the use of hydrogen could by very dangerous as it is ableto generate explosive mixtures with oxygen.

Moreover, it is noted that the compound1-{[(benzyloxy)carbonyl]amino}cyclopropane-1-carboxylic acid, having thefollowing structure:

is the key intermediate for the synthesis of the intermediate 3.

A process for the preparation of the key Intermediate 4 is alsodisclosed in WO 2015/095227A2, wherein said compound is prepared fromthe compound named 1-aminocyclopropane-1-carboxylic acid, having thefollowing structure:

The preparation of the Intermediate 5 is also disclosed in detail inSynthetic communications 22(20) 1992, as a synthetic method involvingfour steps of synthesis, starting from methyl2-diphenylmethyleneaminoacrylate.

The compound named ethyl1-[(diphenylmethylidene)amino]cyclopropane-1-carboxylate having thefollowing structure:

and its preparation is disclosed in detail in the J. Org. Chem. 2005,70, 6976-6979, as a synthetic method involving one step of synthesis,starting from Benzophenoneimine and 1-ethoxycarbonylcyclopropanamine.

SUMMARY OF INVENTION

The problem addressed by the present invention is therefore that ofproviding an improved process for the preparation of7-benzyl-4,7-diazaspiro[2.5]octane-5,8-dione and analogues thereof whichallows to get round to the drawbacks above reported with reference tothe known prior art.

In particular, such improved process should also allow to avoid the useof special and expensive apparatus for carry out the reduction reaction,i.e. the use of autoclaves.

Moreover, such improved process should also allow to avoid the use ofhydrogen atmospheres for carried out the process for preparation of7-benzyl-4,7-diazaspiro [2.5]octane-5,8-dione and analogues thereof.

This problem is solved by a process for the preparation of a saidcompound, which also is a key intermediate for the synthesis ofcompounds having anti-tumor activity, as outlined in the annexed claims,whose definitions and combinations are integral part of the presentdescription.

Further features and advantages of the process according to theinvention will result from the description hereafter reported ofexamples of realization of the invention, provided as an indication andnot as a limitation of the invention.

DESCRIPTION OF EMBODIMENTS

Object of the present invention is a process for the preparation of thecompound of formula (I) or R or S optical isomer thereof:

wherein R₂ is hydrogen, methyl or ethyl, comprising the following steps:

-   -   (a) reaction of the compound of formula (III):

wherein R₁ is C₁₋₄ linear or branched alkyl, with a compound of formula(IV):

wherein R₂ is hydrogen, methyl or ethyl, and wherein X is chosen betweenhydroxyl, halogen or other leaving group; for providing the compound offormula (II) or salt thereof:

wherein R₂ is hydrogen, methyl or ethyl, and wherein R₁ is C₁₋₄ linearor branched alkyl;

-   -   (b) cyclization of the compound of formula (II) obtained in        step (a) to the compound of formula (I):

wherein R₂ is hydrogen, methyl or ethyl.

The compound of formula (I) comprises either the single R enantiomer, orthe S enantiomer, or the racemic mixture or their mixtures in any R/Sratio.

The compound of formula (I) having R configuration is a preferredcompound.

The configurations above described always refers to the configuration ofthe carbon bonded to the R₂ group.

The term of linear or branched C₁₋₄ alkyl thus means an alkyl groupselected among: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,sec-butyl and tert-butyl. Thus, in the compound of formula (III) andcompound of formula (II), R₁ has said meaning.

The compound of formula (III) can be in the form of free base or as asalt. Examples of salts of the compound (III) are those having halidesas counter ions, hence, the salt formed with hydrochloric acid orhybrobromic acid (i.e. compound (III) hydrochloride or hydrobromide).

The compound of formula (II) and compound (IV) can be in the form offree base or as a salt. Examples of salts of the compound (II) and (IV)can be those having halides as counter ions, hence, the salt formed withhydrochloric acid or hybrobromic acid (i.e. compound (II) hydrochlorideor hydrobromide).

The step (a) of the process of the present invention is carried out witha compound of formula (IV) or salts thereof:

wherein X is chosen between hydroxyl, halogen or any group capable toactivate the carboxyl function.

In the compound of formula (IV) halogen is fluorine, chlorine, bromineor iodine.

In the compound of formula (IV), the group capable to activate thecarboxyl function is therefore a group selected among the groupcomprising azides, substituted hydroxylamines (formed, for example, withN-hydroxysuccinimide, 1-hydroxy-benzotriazole), fluoralcoholate esters(formed, for example, with trifluoroethanol), anhydrides (formed, forexample, with pivaloyl chloride, ethyl chloroformate, etc.), esters withphenols (also replaced by electron-attractor groups, for example2-hydroxypyridine), labile amides (formed, for example, with imidazole,triazines, etc.).

According to a preferred embodiment, in the compound of formula (IV) Xis chlorine.

The step a) of the process of the present invention is carried out inpresence of one or more basis.

In particular, the process is carried out in presence of an inorganic oran organic base or a mixture of these.

According to a preferred embodiment, the step a) of the processaccording to the invention can be carried out in the presence of a basesuch as an inorganic base.

The inorganic base that can be used to carry out the step a) of processof the present invention can be chosen among, for example, acetates,bicarbonates, carbonates, hydroxides, phosphates, alcoholates ofalkaline or alkaline-heart metals.

Said inorganic base can also be sodium hydroxide, sodium carbonate,sodium bicarbonate, potassium hydroxide, potassium carbonate, potassiumbicarbonate, caesium hydroxide, caesium carbonate, lithium hydroxide,lithium carbonate, potassium dihydrogen phosphate, potassium hydrogenphosphate, potassium phosphate, sodium dihydrogen phosphate, sodiumhydrogen phosphate or sodium phosphate.

The step a) of process according to the invention can be carried out inthe presence of an organic base such as for example an organic amine ofgeneral formula NR₃ with R being linear or branched C₁₋₇ alkyl andwherein the three R groups can be the same or different. The amine canalso be selected among pyrrolidine, N-alkyl substituted pirrolydine,piperidine, morpholine, N-alkyl substituted piperidine and N-alkylsubstituted morpholine. Suitable bases are, for instance,N-Methlylmorpholine, Triethylamine, diazabicyclooctane (DABCO),Ethyldiisoproprilamine and TMEDA (Tetramethylethylendiamine). TheTriethylamine is preferred since it provides higher molar yields.

The step a) of the process according to the invention can be carried outin the presence of one or more organic solvents such as, for example,toluene, xylene, halogenated solvents, dichloromethane (abbreviatedDCM), dimethylformamide (DMF), N-methylporrolidone (NMP),dimethylsolphoxide (DMSO), tetrahydrofuran (THF), dioxane,methyl-t-butyl ether (MTBE), diethyl ether. Preferably the reaction iscarried out in aromatic solvent or an ether solvent such as toluene,xylene, MTBE, DCM, dioxane, methyl-tetrahydrofuran (Me-THF), THF, beingmore preferred THF and DCM.

The step a) is carried out in an organic solvent, preferably in THF orMe-THF or DCM or toluene mixtures thereof.

The step a) wherein in the compound of formula (IV), X is chlorine canbe conveniently carried out in a solvent being DCM or THF or toluene.

The step a) wherein in the compound of formula (IV), X is chlorine canbe conveniently carried out in DCM and trimethylamine, as base.

The step a) can also be carried out with the compound of formula (IV)wherein X is OH, using, for example, a condensing agent such as acarbodiimide, like, for example, dicyclohexylcarbodiimide, or by meansof propylphosphonic anhydride (T3P), 2-2-chloro methylpyridinium iodide,cyanuric chloride, 2-chloro-4,6-dimethoxy-1,3,5-triazine andphosphonium, uronium and guanidinium salts, etc.

The step b) of the process of the present invention can be carried outby thermal cyclization reaction of the compound of formula (II).

The step b) according can be carried out teachings of the skilled personregarding the synthesis of 2,5-dioxopiperazine by cyclization ofdipeptides.

The step b) is carried out in an organic solvent, preferably in C₃₋₅alcohol or hydrocarbon solvent. Hydrocarbon solvent are, e.g. toluene,xylene, chlorobenzene, tetralyne, heptane, said solvents can also beused for carrying out the step b). More preferably are suitable solventsto carry out the step b) aromatic hydrocarbon solvent or C₄ alcohol,again more preferably toluene, xylene or n-butanol.

The product of formula (I) wherein R₂ is hydrogen obtained in the stepb) can be purified by slurry with water or water containing from 0.01 to0.1% w/w of aqueous hydrochloric acid.

Alternatively or additionally, the product of formula (I) wherein R₂ ishydrogen obtained at the step b) can be purified by crystallization orrecrystallization with acetonitrile or acetonitrile containing from 0.1to 2% w/w of acetic acid, preferably 0.5% w/w. The percentage % w/w isreferred to the weight of acetic acid compared to the weight ofacetonitrile.

The crystallization or recrystallization of compound of formula (I) canbe carried out using from 5 to 15 volumes (V) of acetonitrile (ACN) orACN containing from 0.1 to 2% w/w of acetic acid, preferably 9 volumes(V).

The step b) is carried out at temperature comprised between 60° C. and130° C., preferably between 80° C. and 110° C. or at reflux temperatureof n-butanol (118° C.).

The compound of formula (I) wherein R₂ is hydrogen, prepared accordingto the invention, has a chemical purity higher than 99.80 HPLC A/A % asdetermined by the method HPLC of example 16.

According to a more preferred embodiment of the process, the compound offormula (I) wherein R₂ is hydrogen has chemical purity higher than 99.80HPLC A/A % and each single impurity not more than 0.07%.

The compound of formula (I) wherein R₂ is hydrogen, prepared accordingto the invention, has a chemical purity higher than 99.80 GC A/A % asdetermined by the GC method of example 24.

According to a more preferred embodiment of the process, the compound offormula (I) wherein R₂ is hydrogen has chemical purity higher than 99.80GC A/A % and each single impurity not more than 0.04%.

Moreover, the process according to the present invention could alsoinvolve previous steps for the preparation of the compound of formula(III):

wherein R₁ is C₁₋₄ linear or branched alkyl, said previous steps beingthe following steps:

-   -   a-1) reaction of the compound of formula (VI):

-   -   -   wherein R₁ is C₁₋₄ linear or branched alkyl, with a compound            of formula (VII):

-   -   -   wherein X₁ and X₂ are independently a halogen, mesilate,            tosilate, besilate, or triflate group;        -   to give the compound of formula (V):

-   -   -   wherein R₁ is C₁₋₄ linear or branched alkyl;

    -   b-1) deprotection of the compound of formula (V):

-   -   -   obtained in step a-1) to give the compound of formula (III):

-   -   -   wherein R₁ is C₁₋₄ linear or branched alkyl.

The step a-1) of the process of the present invention is carried outwith a compound of formula (VII):

wherein X₁ and X₂ are independently a halogen, mesilate, tosilate,besilate or triflate.

The halogen of X₁ and X₂ means chorine, fluorine, iodine or bromine.

According to a preferred embodiment of the process, the compound offormula (VII) is the one in which X₁ and X₂ are both chlorine, bromineor iodine.

According to a more preferred embodiment of the process, the compound offormula (VII) is the one in which X1 and X2 are both bromine, since itprovides higher molar yields.

According to a preferred embodiment, the step a-1) of the process iscarried out using from 2.5 to 3.5 molar equivalents of the compound offormula (VII) in which X1 and X2 are both bromine, referenced to thecompound of formula (VI), more preferably about 3.0 molar equivalentssince it provides higher molar yields of the compound of formula (V).

The step a-1) of the process of the present invention is carried out inpresence of one or more basis.

In particular, the step a-1) of the process is carried out in presenceof an inorganic or an organic base or a mixture of these.

According to a preferred embodiment, the step a-1) of the processaccording to the invention can be carried out in the presence of a basesuch as an inorganic base.

The inorganic bases used to carry out the step a-1) of process of thepresent invention can be chosen among, for example, acetates,bicarbonates, carbonates, hydroxides, phosphates, alcoholates orhydrides of alkaline or alkaline-heart metals.

Said inorganic base can also be sodium hydroxide, sodium hydride, sodiumcarbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate,potassium bicarbonate, caesium hydroxide, caesium carbonate, lithiumhydroxide, lithium carbonate, potassium dihydrogen phosphate, potassiumhydrogen phosphate, potassium phosphate, sodium dihydrogen phosphate,sodium hydrogen phosphate, sodium phosphate. The sodium hydride,potassium hydroxide, potassium carbonate and cesium carbonate arepreferred since it provides higher molar yields.

According to a more preferably embodiment, the step a-1) of the processaccording to the invention can be carried out in the presence of sodiumhydride or sodium hydride 60% on mineral oil or potassium hydroxide.

The process according to the invention can be carried out in thepresence of an organic base such as, for example, an organic amine ofgeneral formula NR₃ with R being linear or branched C₁₋₇ alkyl andwherein the three R groups can be the same or different. The amine canalso be selected among pyrrolidine, N-alkyl substituted pirrolydine,piperidine, morpholine, N-alkyl substituted piperidine and N-alkylsubstituted morpholine. Suitable bases are for instanceN-Methlylmorpholine, Triethylamine, DABCO, Ethyldiisoproprilamine andTMEDA (Tetramethylethylendiamine). The Triethylamine is preferred sinceit provides higher molar yields.

The step a-1) of the process of the present invention can be optionallycarried out in presence of a phase transfer catalyst.

Said phase transfer catalyst can be, for example, an organic ammoniumsalt of general formula NR₄X wherein X is hydroxyl or halogen and R islinear or branched C₁₋₁₂ alkyl, aryl or substituted aryl, and the four Rgroups can be the same or different. The triethylbenzilamminium chlorideis preferred since it provides higher molar yields.

The step a-1) according to the invention can be carried out in thepresence of one or more solvents such as e.g. toluene, xylene, DMF, NMP,DMSO, THF, Dioxane, MTBE, diethyl ether.

Preferably the reaction of step a-1) is carried out in an aromaticsolvent or an ether solvent such as, for example, toluene, xylene,methyl-t-butyl ether (MTBE), Dioxane, methyl-THF, tetrahydrofuran (THF).

According to a more preferably embodiment, the step a-1) of the processaccording to the invention is carried out in an aromatic solvent.

According to an again more preferably embodiment, the step a-1) of theprocess according to the invention, is carried out in a hydrocarbonaromatic solvent.

According to a more preferably embodiment, the step a-1) of the processaccording to the invention is carried out in toluene or xylene.

The step a-1) according to the invention can be carried out in thepresence of sodium hydride or sodium hydride 60% on mineral oil one inan aromatic solvent, preferably, in a hydrocarbon aromatic solvent.

The step a-1) according to the invention can be carried out in thepresence of sodium hydride or sodium hydride 60% on mineral oil one intoluene.

According to a preferred embodiment, the step b-1) of the process iscarried out using from 2.5 to 3.5 molar equivalents of sodium hydride orsodium hydride 60% in mineral oil, referenced to the compound of formula(VI), more preferably about 3.0 molar equivalents since it provideshigher molar yields of the compound of formula (V).

According to a preferred embodiment, the step a-1) of the processaccording to the invention can be carried out at temperature between 0to 20° C., more preferably between 5 to 10° C.

The step b-1) according to the invention can be carried out in thepresence of acetic acid.

The step b-1) according to the invention can be carried out in thepresence of one or more solvents such as toluene, xylene, DMF, NMP,DMSO, Dioxane, MTBE, water, acetic acid, and mixture of water and aceticacid.

The step b-1) according to the invention can also be carried out in thepresence of acetic acid in an aromatic solvent such as toluene.

According to a preferable embodiment, the step b-1) of the process ofthe invention is carried out in a mixture of acetic acid and water.

According to a preferred embodiment, the step b-1) of the process iscarried out using from 1 to 2 molar equivalents of acetic acid,referenced to the compound of formula (V), more preferably about 1.65molar equivalents since it provides higher molar yields of the compoundof formula (III).

According to a preferred embodiment, the step b-1) of the processaccording to the invention can be carried out at temperature between 30to 80° C., preferably between 40° C. and 60° C., more preferably at 50°C.

The compound of formula (VI), can be prepared according to the followingreaction scheme:

The above commercially available compound (VI) can be prepared forexample by chemical condensation of glycine ester with benzophenone asdescribed in literature.

The preparation of the compound of formula (VI) can be performedapplying the teachings of Synlett, 2016, 27(9), 1403-1407; Journal ofthe American Chemical Society, 2015, 137(45), 14446-14455; AngewandteChemie, International Edition, 2013 52(49), 12942-12945; OrganicLetters, 2012 14(2), 552-555.

Moreover, the process according to the present invention, can alsocomprise the further step c) of reduction of the compound, obtained instep b), of formula (I):

wherein R₂ is hydrogen, methyl or ethyl, to give the compound of formula(I-bis):

wherein R₂ is hydrogen, methyl or ethyl.

Said further reduction step can be carried out applying the teachings ofthe skilled person regarding the reduction of carbonyl groups. Inparticular, the reduction can be carried out in presence of BH₃/THFcomplex in THF.

In particular, the reduction in presence of BH₃/THF complex in THF canbe carried out at 0° C., according to the teaching of EP2380892A,example 3, Step 3, or according to the teaching of Bioorganic &Medicinal Chemistry 23 (2015) 2360-2367.

The following schema 1 summarizes the overall process of the invention:

The process of the present invention thus provides new intermediates,i.e. the compound of formula (II):

wherein R₂ is hydrogen, methyl or ethyl, and wherein R₁ is C₁₋₄ linearor branched alkyl and the configuration of the stereocenter of R₂ is Ror S or R/S mixture, or racemate;

with the exception of the compound of formula (II) wherein R₂ ishydrogen and R₁ is methyl.

According to a preferred embodiment, the compound of formula (II):

has the following formula:

wherein R₁ is C₁₋₄ linear or branched alkyl.

The process of the present invention thus also provides newintermediates, i.e. the compound of formula (V):

wherein R₁ is C₃₋₄ linear or branched alkyl.

The compound of formula (II), (III), (V), (X):

wherein in the compound of formula (II) and (X) R₂ is hydrogen, methylor ethyl, and wherein in each of the compounds R₁ is C₁₋₄ linear orbranched alkyl; with the exception of the compounds:

of formula (II) wherein R₂ is hydrogen and R₁ is methyl;

of formula (III) wherein R₁ is methyl;

can be used for the preparations of compound of formula (I) or R or Soptical isomer, and the compound of formula (I-bis) or R or S opticalisomer, or salt thereof:

wherein R₂ in compound (I) and (I-bis) is hydrogen, methyl or ethyl.

According to a preferred embodiment, the following compound of formula(II-a), (II-b), (II-c), (II-d), (III-a), (V-a), (X-a), (X-b), (X-d):

can be used for the preparations of the following compound of formula(I-a/d) and (I-bis-a/d) or salt thereof:

Therefore, the compound of formula (II), (III), (V), (X):

wherein in the compound of formula (II) R₂ is hydrogen, methyl or ethyl,and wherein in each of the compound R₁ is C₁₋₄ linear or branched alkyl;can be used for the for the preparations of compound of formula (VIII)or R or S optical isomer, or salt thereof:

wherein R₂ is hydrogen, methyl or ethyl.

According to a preferred embodiment, the process mentioned can also besummarize by the following Schema 2:

Thus, according to a preferred embodiment, the compound of formula (II)having the formula:

wherein R₁ is C₁₋₄ linear or branched alkyl;

can be used for the preparations of compound of formula (VIII) whereinR₂ is ethyl an is in R optical configuration.

The compounds of formula (I), (I-bis), (II), (IV) and (VIII) compriseeither the R enantiomer, or the S enantiomer, or the racemic mixture ortheir mixtures in any R/S ratio.

The compound of formula (I), (I-bis), (II), (IV) and (VIII) having Rconfiguration is a preferred compound.

The configurations above described always refers to the configuration ofthe carbon bonded to the R₂ group.

The compounds of formula (I) or of formula (I-bis) wherein R₂ ishydrogen methyl or ethyl are preferred since they are those involved inthe preparation of marketed active pharmaceutical ingredients (API).

All the features and preferred embodiments of the process of the presentinvention given above can be combined in each possible combination tocarry out the claimed process.

All of the intermediates and compounds of the present invention inparticular those of formula (V), (III), (IV), (II), (I), (I-bis) can bein isolated or in not isolated form, from the reaction mixture whereinthey are prepared.

According to the preferred embodiment, all of the intermediates andcompounds isolated are typically in form of a solid or of an isolatedoil.

According to the preferred embodiment, all of the intermediates andcompounds not isolated are typically in form of solution with an organicsolvent or water.

In an alternative embodiment, the compound of formula (II) can besynthesized according to the following Schema 3:

wherein R₂ is hydrogen, methyl or ethyl, and wherein R₁ is C₁₋₄ linearor branched alkyl;

The compound of formula (II) as well as the compound of formula (X)comprises either the single R enantiomer, or the S enantiomer, or theracemic mixture or their mixtures in any R/S ratio.

The compound of formula (II) as well as the compound of formula (X)having R configuration is a preferred compound.

The configurations above described always refers to the configuration ofthe carbon bonded to the R₂ group.

The step a-bis-1 of the process of the present invention can be carriedout in presence of one or more basis.

In particular, the process is carried out in presence of an inorganic oran organic base or a mixture of these.

According to a preferred embodiment, the step a-bis-1 of the processaccording to the invention can be carried out in the presence of a basesuch as an organic base.

The inorganic base that can be used to carry out the step a-bis-1 ofprocess of the present invention can be chosen among, for example,acetates, bicarbonates, carbonates, hydroxides, phosphates, alcoholatesof alkaline or alkaline-heart metals.

Said inorganic base can also be sodium hydroxide, sodium carbonate,sodium bicarbonate, potassium hydroxide, potassium carbonate, potassiumbicarbonate, caesium hydroxide, caesium carbonate, lithium hydroxide,lithium carbonate, potassium dihydrogen phosphate, potassium hydrogenphosphate, potassium phosphate, sodium dihydrogen phosphate, sodiumhydrogen phosphate or sodium phosphate.

The step a-bis-1 of process according to the invention can be carriedout in the presence of an organic base such as for example an organicamine of general formula NR₃ with R being linear or branched C₁₋₇ alkyland wherein the three R groups can be the same or different. The aminecan also be selected among pyrrolidine, N-alkyl substituted pirrolydine,piperidine, morpholine, N-alkyl substituted piperidine and N-alkylsubstituted morpholine. Suitable bases are, for instance,N-Methlylmorpholine, Triethylamine, diazabicyclooctane (DABCO),Ethyldiisoproprilamine and TMEDA (Tetramethylethylendiamine). TheTriethylamine is preferred since it provides higher molar yields.

The step a-bis-1 of the process according to the invention can becarried out in the presence of one or more organic solvents such as, forexample, toluene, xylene, halogenated solvents, dichloromethane(abbreviated DCM), dimethylformamide (DMF), N-methylporrolidone (NMP),dimethylsolphoxide (DMSO), tetrahydrofuran (THF), dioxane,methyl-t-butyl ether (MTBE), diethyl ether, acetate such as, forexample, ethylacetate, methylacetate, propylacetate, isobutylacetate,isopropylacetate. Preferably the reaction is carried out in acetatesolvent such as ethylacetate (abbreviate EcOAc), methylacetate,isopropylacetatetoluene, being more preferred EtOAc.

The step a-bis-1 is carried out in an organic solvent, preferably inEtOAc.

The step a-bis-1 can also be carried out with the compound of formula(IV), using, for example, a condensing agent such as a carbodiimide,like, for example, dicyclohexylcarbodiimide, or by means of phosgenationagent.

The phosgenation agent can be chosen between phosgene,dichloromethylcloroformate (Diphosgene), triphosgene,Carbonyldiimidazole, etc.

The step a-bis-1 is carried out using, for example, a condensing agent,preferably with phosgenation agent, more preferably with triphosgene.

The step a-bis of the process of the present invention is carried out inpresence of one or more basis.

In particular, the process is carried out in presence of an inorganic oran organic base or a mixture of these.

According to a preferred embodiment, the step a-bis of the processaccording to the invention can be carried out in the presence of a basesuch as an inorganic base.

The inorganic base that can be used to carry out the step a-bis ofprocess of the present invention can be chosen among, for example,acetates, bicarbonates, carbonates, hydroxides, phosphates, alcoholatesof alkaline or alkaline-heart metals.

Said inorganic base can also be sodium hydroxide, sodium carbonate,sodium bicarbonate, potassium hydroxide, potassium carbonate, potassiumbicarbonate, caesium hydroxide, caesium carbonate, lithium hydroxide,lithium carbonate, potassium dihydrogen phosphate, potassium hydrogenphosphate, potassium phosphate, sodium dihydrogen phosphate, sodiumhydrogen phosphate or sodium phosphate.

The step a-bis of process according to the invention can be carried outin the presence of an organic base such as for example an organic amineof general formula NR₃ with R being linear or branched C₁₋₇ alkyl andwherein the three R groups can be the same or different. The amine canalso be selected among pyrrolidine, N-alkyl substituted pirrolydine,piperidine, morpholine, N-alkyl substituted piperidine and N-alkylsubstituted morpholine. Suitable bases are, for instance,N-Methlylmorpholine, Triethylamine, diazabicyclooctane (DABCO),Ethyldiisoproprilamine and TMEDA (Tetramethylethylendiamine). TheTriethylamine is preferred since it provides higher molar yields.

The step a-bis of the process according to the invention can be carriedout in the presence of one or more organic solvents such as, forexample, toluene, xylene, halogenated solvents, dichloromethane(abbreviated DCM), dimethylformamide (DMF), N-methylporrolidone (NMP),dimethylsolphoxide (DMSO), tetrahydrofuran (THF), dioxane,methyl-t-butyl ether (MTBE), diethyl ether. Preferably the reaction iscarried out in aromatic solvent or an ether solvent such as toluene,xylene, MTBE, DCM, dioxane, methyl-tetrahydrofuran (Me-THF), THF, beingmore preferred THF and DCM.

The step a-bis is carried out in an organic solvent, preferably in THFor Me-THF or DCM or toluene mixtures thereof.

The step a-bis wherein in the compound of formula (IV) can beconveniently carried out in a solvent being DCM or THF or toluene.

The step a-bis wherein in the compound of formula (IV) can beconveniently carried out in DCM and trimethylamine, as base.

The step a-bis of the process according to the invention can be followedby the step b), previously described, for carrying out the cyclisationof the compound of formula (II) to the compound of formula (I).

EXPERIMENTAL SECTION

The starting material DPMGE, dibromoethane and N-benzyl glycine, arereactants largely commercially available, for example, for supplied bySigma-Aldrich.

Volumes means volume of solvent per unit of product, thus, for example,1 volume is 1 Liter per 1 Kilo, or 1 mL for 1 gram, or 1 microliter per1 milligram. Thus, 10 volumes means for example 10 liters per 1 Kilogramof substance.

Example 1: Synthesis of the Compound of Formula (V) in which R₁ is Ethyl

To a mixture of DPMGE (40 g, 150 mmol), KOH (41.9 g, 750 mmol), K₂CO₃(41.4 g, 300 mmol), CsCO₃ (7.32 g, 22.5 mmol), TEBAC (6.82 g, 30 mmol)in methylisobutyl ketone (250 ml) was added in around 40 min. a solutionof 1,2-dibromoethane (33.76 g, 180 mmol) at 0° C. and the reaction wasstirred at the same temperature for 16 hours. The obtained reactionmixture was filter and the filtrate containing the compound (V) was useddirectly in the next step.

Example 2: Synthesis of the Compound of Formula (III) in which R₁ isEthyl

To a mixture of the organic solution obtained in the Example 1 and water(200 ml) and was added a solution of 1M HCl until the pH is 3. Thereaction mixture was stirred at room temperature until the reaction wascomplete (the compound (V) was disappearing, IPC by TLC ethylacetate:petroleum ether=1:3). Then, the reaction mixture was extractwith MIBK (100 mL) for three times. To the obtained aqueous mixture wasadded DCM (200 mL) and the pH was brought to 9 by adding a solution of10% NaOH. Then, the obtained mixture was extracted with DCM (100 mL) forthree times. The combined organic layer was concentrated on vacuum togive product (III) (8.7 g, 45% overall yield of 2 steps) as apale-yellow oil.

Example 3: Synthesis of the Compound of Formula (V) in which R₁ is Ethyl

To a solution of DPMGE (350 g, 1.31 mol) in toluene (1 L) was added inaround 40 min. a suspension of sodium hydride (60% in mineral oil, 78.65g, 1.95 mol) in toluene (750 mL). The mixture was heated at 110° C. andwas stirred for 1 h. To the obtained reaction mixture was added1,2-dibromoethane (738.4 g, 3.9 mol) and the reaction was stirred at thesame temperature for 3 hours. To the obtained reaction mixture was addeda suspension of sodium hydride (60% in mineral oil, 78.65 g, 1.95 mol)in toluene (750 mL). The mixture was stirred at 110° C. for 4 h. Theobtained reaction mixture was cooled to 5-10° C. and was slowly dosedwater (1.4 L). The obtained mixture was stirred for 1 hour at roomtemperature. The aqueous solution was spit-off and the obtaining organicsolution containing the compound (V) was used directly in the next step.The GC purity according to the method of example 16 is 80-85%.

Example 4: Synthesis of the Compound of Formula (III) in which R₁ isEthyl

To the organic solution obtained in the Example 1 was added a solutionof acetic acid (130 g, 2.16 mol) in water (5 L). The reaction mixturewas heated a T=50° and was stirred for 10-13 hours or until the reactionwas complete (the compound (V) was disappearing, IPC by TLC ethylacetate:petroleum ether=1:3). Then, the reaction mixture was cooled toroom temperature and the phase was spitted. The obtaining aqueoussolution containing the compound (III) was used directly in the nextstep. Alternatively, to the obtained aqueous mixture was added DCM (1 L)and the pH was brought to 9 by adding a solution of 10% NaOH. Then, theobtaining mixture was extracted with DCM (1 L) for three times. Thecombined organic layer was concentrated on vacuum to give product (III)(84.55 g, 50% overall yield of 2 steps) as a pale-yellow oil.

Example 5: Synthesis of the Compound of Formula (IV) in which R₂ isHydrogen and X is Chlorine

To a suspension of PCl₅ (1.51 g, 7.25 mmol) in Toluene (30 ml, 30 V) wasadded benzyl-glycine (1 g, 6.05 mmol). The reaction mixture was stirredat r.t. for 6 h. To the obtained reaction mixture was filtered and theobtained solid was washed with DCM (10 mL) for two times. The obtainingsolid was dried on vacuum to give product (IV) hydrochloride salt (1.25g, 93% yield) as a white solid.

Example 6: Synthesis of the Compound of Formula (II) in which R₁ isEthyl and R₂ is Hydrogen

To a suspension of compound (IV) (0.16 g, 0.7 mmol) and compound (III)(wherein R₁ is ethyl, 0.1 g, 0.6 mmol) in DCM (2.50 ml) was added slowlyTEA (0.21 g, 2 mmol). The reaction was stirred at r.t. for 3 hours, thenthe solvent was concentrated under reduced pressure. The residueobtained was diluted with ethyl acetate, washed with saturated aqueoussodium bicarbonate solution and saturated brine, and then dried overanhydrous sodium sulphate. The solvent was evaporated under reducedpressure and the residue obtained was purified by silica gel columnchromatography to give the title compound (27 mg, 16%). 1H-NMR (500 MHz,DMSO-d₆): 1.00-1.03 (2H, m), 1.14 (3H, t, J=7 Hz), 1.33-1.36 (2H, m),2.56 (1H, brs), 3.06 (2H, s), 3.68 (2H, s), 4.37 (2H, q, J=7 Hz),7.23-7.32 (5H, m), 8.38 (1H, s). 13C-NMR (125 MHz, DMSO-d₆): 172.26;172.02; 140.24; 128.07; 128.01; 126.60; 60.52; 52.34; 51.17; 40.00;39.83; 39.76; 39.67; 39.50; 39.33; 39.16; 39.00; 32.58; 16.59; 14.00.

Example 7: Synthesis of the Compound of Formula (I) in which R₂ isHydrogen

A solution of compound (II) (wherein R₁ is ethyle) (1.2 kg, 4.34 mol) inn-Butanol (4.8 L, 4V) was heated at T of reflux and stirred for 10 h.Then, the reaction mixture was cooled slowly to T=5-10° C. and stirredat this temperature for 1 h. The obtaining suspension was filtered andthe obtaining solid was washed with n-heptane (300 mL) for three times.To the obtained cake was added a solution of HCl (35%, 10.7 g) in water(3.7 kg, 3V) and the obtaining mixture was stirred at r.t. for 2 h.Then, the mixture was cooled to 5-10° C. and stirred for 1 h. Theobtaining suspension was filtered and washed with water (400 mL) forthree times. The obtaining solid was dried on vacuum to give crudeproduct (1) (770 g, GC purity 98.9%, HPLC purity 99.2%) as a whitesolid.

The obtained crude product (I) was recrystallized from a mixture ofacetonitrile (7.11 kg) and acetic acid (38.5 g), the obtainingsuspension was heated at temperature of reflux to give a clearpale-yellow solution. Then, the solution was cooled to 5-10° C. andstirred for 1 h. The obtaining suspension was filtered and washed withacetonitrile (100 mL) for three times. The obtaining solid was dried onvacuum to give product (I) (690 g, 69% yield and 97% yield of therecrystallization, HPLC purity 99.84%, max single impurity 0.07%; GCpurity 99.86%, max single impurity 0.04%) as a white solid.

Example 8: Synthesis of the Methyl Ester of the Compound of Formula (IV)in which R₂ is Ethyl in R Configuration (Compound (IV-a))

The compound of formula (IV-a) was synthesized according to the teachingof Tetrahedron 57(2001), 6589-6605.

Example 9: Synthesis of the Compound of Formula (IV) in which R₂ isEthyl in R Configuration (Compound (IV-b))

A solution of compound (IV-a) (1 g, 4.82 mmol) was dissolved in amixture of aq HCl (5 mL, 20%) and dioxane (5 mL) and stirred for 3 daysat 60° C. Evaporation of the solvent in vacuo gave compound (IV-b) (922mg, 99% yield).

Example 10: Synthesis of the Compound of Formula (I) in which R₂ isEthyl (Intermediate 3)

The Intermediate 3 was synthesized according to the procedures givenfrom example 5 to example 7, starting from (R)-2-benzylamino-butanoicacid (compound (IV-b)) obtained in the Example 9. The productintermediate 3 has been characterized by NMR. 1H-NMR (400 MHz, DMSO-d6):0.93-0.98 (2H, m), 0.99 (3H, t, J=7.6 Hz), 1.35-1.40 (1H, m), 1.80-1.86(1H m), 1.91-1.98 (2H, m), 3.89 (1H, t, J=5.2 Hz), 3.94 (1H, d, J=14.9Hz), 5.35 (1H, d, J=14.9 Hz), 7.25-7.35 (5H, m), 7.51 (1H, brs). MS(ESI) m/z: 259 [(M+1)⁺].

Example 11: Synthesis of the Compound of Formula

A solution of borane-tetrahydrofuran complex in THF (0.93 M, 375 ml, 350mmol) was added to a THF (200 ml) solution of the Intermediate 3 (22.42g, 86.8 mmol) prepared in example 10 under ice cooling and then theresulting mixture was heated to reflux for 19 hours. Methanol (130 ml)was added to the reaction mixture under ice cooling, the resultingmixture was stirred for 60 minutes and then the solvent was concentratedunder reduced pressure. Ethanol (400 ml), water (100 ml), andtriethylamine (150 ml) were added to the residue obtained, the resultingmixture was heated to reflux for 2 hours and then the solvent wasconcentrated under reduced pressure. The residue obtained was dilutedwith ethyl acetate, washed with saturated aqueous sodium bicarbonatesolution and saturated brine, and then dried over anhydrous sodiumsulphate. The solvent was evaporated under reduced pressure and theresidue obtained was purified by silica gel column chromatography[chloroform:methanol=10:1 (v/v)] to give the title compound (11.20 g,59%).

Example 12: Synthesis of the Compound(6R)-7-benzyl-6-ethyl-4-(trifluaraacetyl)-4,7-ciiazaspira[2.5]actane, ofFormula

Trifluoroacetic anhydride (8.35 ml, 60 mmol) was added dropwise to adichloromethane (200 ml) solution of the compound obtained in theexample 11 (11.20 g, 50 mmol) and triethylamine (16.7 ml, 120 mmol)under ice cooling and the resulting mixture was stirred at the sametemperature for 1 hour. Saturated aqueous sodium bicarbonate solutionwas added to the reaction mixture and the resulting mixture was dilutedwith chloroform, then washed with saturated brine, and dried averanhydrous sodium sulphate. The solvent was evaporated under reducedpressure to give the title compound (16.15 g, 99%) as a colourless oil.1H-NMR (400 MHz, DMSO-d₆): 0.65-0.70 (1H, m), 0.85-0.90 (2H, m), 0.91(3H, t, J=7.4 Hz), 1.18-1.23 (1H, m), 1.46-1.53 (1H m), 1.66-1.75 (1H,m), 2.31-2.36 (1H, m), 2.38-2.45 (2H, m), 3.32 (1H, d, J=13.9 Hz),3.40-3.47 (1H, m), 3.84 (1H, d, J=11.7 Hz), 3.97 (1H, d, J=13.9 Hz),7.18-7.23 (1H, m), 7.27-7.31 (4H, m). MS (ESI) m/z: 327 [(M+H)⁺].

Example 13: Synthesis of the Compound(6R)-6-ethyl-4-(trifluaraacetyl)-4,7-ciiazaspira[2.5]actanehycirachlaricie, of Formula

A solution of 1 N hydrochloric acid in ethanol (100 ml, 100 mmol) and 5%palladium on carbon (3 g) were added to an ethanol (250 ml) solution ofthe compound (15 g, 46 mmol) obtained in Example 12 above and theresulting mixture was subjected to catalytic reduction for 15 hours in ahydrogen atmosphere. The catalyst was removed by filtration throughcelite and then the filtrate was concentrated under reduced pressure. Anethanol/diethyl ether mixed solvent was added to the residue obtainedand the deposited solid was collected by filtration to give the titlecompound (10.67 g, 85%) as a colourless solid. 1H-NMR (400 MHz,DMSO-d₆): 0.89-0.94 (1H, m), 0.99 (3H, t, J=7.6 Hz), 1.16-1.21 (1H, m),1.25-1.31 (1H, m), 1.41-1.48 (1H, m), 1.66-1.74 (1H, m), 1.77-1.85 (1H,m), 2.86 (1H, d, J=12.9 Hz), 3.24-3.32 (1H, m), 3.37-3.44 (1H, m), 3.45(1H, d, J=12.9 Hz), 4.06-4.14 (1H, m). MS (ESI) m/z: 237 [(M+H)⁺].

Example 14: Synthesis of Intermediate 2 Named(6R)-6-ethyl-7-[(4R)-4-fluara-L-pralyl]-4-(trifluaraacetyl)-4,7-ciiazaspira[2.5]actanehave Formula

The compound was synthesized, starting from the compound obtained inexample 13, according to the teaching of EP2380892B, reference example11.

Example 15: Synthesis of the Compound of Formula (VIII) in which R₂ isR-Ethyl, i.e. Compound (IX)

The compound was synthesized, starting from the compound obtained inexample 14, according to the teaching of EP2380892B, Example 5 andExample 6.

Example 16: Synthesis of the Compound of Formula (II) in which R₁ isEthyl and R₂ is Hydrogen, i.e. Compound (II-a)

To a solution of triphosgene (3.6 g, 0.4 eq) in ethyl acetate (i.e.EtOAc) (200 ml, 40V) was added N-Benzyl glycine (5 g, 1 eq). Then asolution of triethylamine (3.37 g, 1.1 eq) in EtOAc (50 ml, 10V) wasadded dropwise over a period of 40 min, and the mixture was stirred foranother 4 h. The obtained reaction mixture was filtered and concentrateunder vacuum to give the compound of formula (X-a) 3.64 g, yield 63%,HPLC purity 96.43%. It was dissolved in CH₂Cl₂ (i.e. DCM) (25 ml, 5V),reserved.

In a 50 ml glass reactor, was charged compound (III) (wherein R1 isethyl, 3.5 g, 0.7 eq), triethylamine (4.29 g, 1.4 eq) and CH₂Cl₂ (25 ml,5V). the obtained solution was added dropwise to the DCM solution ofcompound of formula (X-a). After adding, the mixture was stirred for 7h. Then water (50 ml, 10V) was charged and the phase was separated. Theorganic layer was extracted with 2N aqueous HCl (20 ml×2, 8V). Theaqueous phase was adjusted to pH 8 with sodium bicarbonate. Then theobtained solution was extracted with DCM (25 ml×2, 10V). The aqueousphase was concentrated under reduced pressure to obtain compound (II)(in which R₁ is Ethyl) 2.17 g, yield 41.3%, GC purity 60%.

Example 17: Synthesis of the Compound of Formula (I) in which R₂ isHydrogen

To a solution of compound (II) (wherein R1 is ethyl) (0.67 g, 1 eq) inbutyl alcohol (3.3 ml, 5V) was added acetic acid (0.13 g, 20% wt). Themixture was refluxed for 10 h. After the reaction was complete, n-Hexane(5.4 ml, 8V) was added to the mixture. The obtained suspension wasfiltered and washed with n-Hexane (1.3 ml, 2V). The obtaining off-whitesolid was dried on vacuum to give product (I) 0.2 g, yield 36%, GCpurity 98.44%.

Example 18: Synthesis of the Compound of Formula (IV) in which R₂ isEthyl in R Configuration (Compound (IV-b))

A mixture of (R)-2-aminobutanoic acid (5 g, 1 eq), aqueous sodiumhydroxide solution (2 mol/L, 24 ml, 1 eq) and benzaldehyde (5.15 g, 1eq) was stirred at 25° C. for 4 hours. Then the resulting mixture wascooled to 0° C., and to the mixture was added sodium borohydride (1.05g, 0.57 eq) in portions. After the addition, the resulted mixture wasstirred at 25° C. for 12 hours. After the reaction was finished, thereaction mixture was extracted with DCM (10 ml×3). The organic phaseswere discarded. The water phase was adjusted to pH 5-6 with concentratedhydrochloric acid, then the mixture was filtrated to give the product asa white solid 5.8 g, yield 62%, HPLC purity 98.33%, [α]Dr.t.=−14.6(c=0.4 g/100 ml, H₂O).

Example 19: Synthesis of the Compound of Formula (II) in which R₁ isEthyl and R₂ is Ethyl in R Configuration (Compound (II-c))

To a solution of triphosgene (1.96 g, 0.4 eq) in EtOAc (128 ml, 40V) wasadded the R-2-ethyl-N-Bn glycine (compound IV-b, 3.2 g, 1 eq). Then amixture of Triethylamine (1.84 g, 1.1 eq) in EtOAc (32 ml, 10V) wasadded dropwise to the solution over a period of 40 min, and the mixturewas stirred for another 4 h. The reaction mixture was filtered andevaporated to give the compound of formula (X-b) 2.54 g, yield 70%, HPLCpurity 93.6%. It was dissolved in DCM (16 ml, 5V).

To a 50 ml glass reactor, added amino ester hydrochloride (1.92 g, 0.7eq), Triethylamine (2.35 g, 1.4 eq) and DCM (16 ml, 5V). Filtered andfiltrate was added dropwise to the solution of compound of formula(X-b). After adding, the mixture was stirred for another 7 h. water (32ml, 10V) was charged and separated. The organic layer was extracted with2N HCl aq (12.8 ml×2). The aqueous phase was adjusted to pH 8 withsodium bicarbonate. The solution was extracted with DCM (16 ml×2) andconcentrated under reduced pressure to obtain compound (II-c) 1.58 g,yield 45%, GC purity 62%. The structure was confirmed by GC-MS.

Example 20: Synthesis of the Compound of Formula (I) in which R₂ isEthyl (Intermediate 3)

To a solution of compound (II-c) (0.7 g, 1 eq) in butyl alcohol (3.5 ml,5V) was added acetic acid (0.14 g, 20% wt). The mixture was refluxed for10 h. After the reaction was complete, the reaction solution wasconcentrated under reduced pressure. The residue was chromatographed(EtOAc:n-Hexane=1:2) to get the intermediate 3 as a yellow oil 0.25 g,yield 42.4%, GC purity 98.42%. [α]Dr.t.=−63 (c=0.4 g/100 ml, CH₃OH).

Example 21: Synthesis of the Compound of Formula (IV) in which R2 isMethyl in R Configuration (Compound (IV-c))

A mixture of (R)-2-aminopropanoic acid (5 g, 1 eq) in aqueous sodiumhydroxide (2 mol/L, 28 ml, 1 eq) and benzaldehyde (6 g, 1 eq) wasstirred at 25° C. for 4 hours. Then the mixture was cooled to 0° C., andto the mixture was added sodium borohydride (1.21 g, 0.57 eq) inportions. After the addition, the resulted mixture was stirred at 25° C.for 12 hours. After the reaction was finished, the reaction mixture wasextracted with DCM (10 ml×3). The organic phases were discarded and thewater phase was adjusted to pH 5-6 with concentrated hydrochloric acid,then the mixture was filtrated to give the compound (II-c) as a whitesolid 4.27 g, yield 42.5%, HPLC purity 99.12%, [α]Dr.t.=−15 (c=0.4 g/100ml, H₂O).

Example 22: Synthesis of the Compound of Formula (II) in which R₁ isMethyl and R₂ is Ethyl in R Configuration

To a solution of triphosgene (3.15 g, 0.4 eq) in EtOAc (190 ml, 40V) wasadded the compound (IV-c) (4.75 g, 1 eq), Triethylamine (2.95 g, 1.1 eq)in EtOAc (47.5 ml, 10V) was added dropwise to the solution over a periodof 40 min, and the mixture was stirred for another 4 h. The reactionmixture was filtered and evaporated to give the compound of formula(X-c) 3.26 g, yield 60%, HPLC purity 89.34%. It was dissolved in DCM(23.4 ml, 5V), reserved.

To a 50 ml glass reactor, added compound (111) hydrochloride (3.07 g,0.7 eq), Triethylamine (3.75 g, 1.4 eq) and DCM (23.4 ml, 5V). Filteredand filtrate was added dropwise to the solution of compound of formula(X-c). After adding, the mixture was stirred for another 7 h. Water(47.5 ml, 10V) was charged and the phase was separated. The organiclayer was extracted with 2N HCl aq (19 ml×2). The obtaining aqueousphase was adjusted to pH 8 with sodium bicarbonate and the solution wasextracted with DCM (23.4 ml×2). The obtained aqueous phase wasconcentrated under reduced pressure to obtain compound (II) (in which R₁is Methyl and R₂ is Ethyl in R configuration) 2.05 g, yield 44.4%, GCpurity 80.3%.

Example 23: Synthesis of the Compound of Formula (I) in which R₂ isMethyl

To a solution of compound obtained in the example 22 (2.05 g, 1 eq) inbutyl alcohol (10.25 ml, 5V) was added acetic acid (0.41 g, 20% wt). Themixture was refluxed for 10 h. After the reaction was complete, thereaction solution was concentrated under reduced pressure. The residuewas chromatographed (EtOAc:n-Hexane=1:2) to get the product as yellowoil 1.07 g, yield 62.2%, GC purity 88.8%. [α]Dr.t.=−27.3 (c=0.4 g/100ml, CH₃OH).

Example 24: Analytic Method for Determining the Chemical Purity and theAmount of Impurities of the Present Invention

Method A: method for monitoring the reaction of example from 1 to 5, viathe following HPLC method:

Column Intersil ODS-3 150 * 4.0 mm, 3 μm Temp. Column 30° C. MobilePhase A 1.0 g potassium dihydrogen phosphate in 1000 mL water, adjust pHto 7.0 with NaOH Mobile Phase B Acetonitrile Gradient Time (min) % A % B0.01 95.0 5.0 15.00 50.0 50.0 25.00 10.0 90.0 30.00 10.0 90.0 30.01 95.05.0 35.00 95.0 5.0 Run Time 35.0 min Flow 1.0 mL/min UV Detector 210nm(main)/254 nm Injection Volume 5 μL Analysis Time 30.0 min DiluentAcetonitrile

Method B: method for monitoring the reaction of example 6 and 7 and thepurity of the compound of formula (I) wherein R₂ is hydrogen, via thefollowing HPLC method:

Column XBridge Shield RP18(250 * 4.6 mm, 5 μm) Temp. Column 20° C.Mobile Phase A 1.0 g Ammonium dihydrogen phosphate and 5 ml Ammoniumhydroxide in 1000 mL water, adjust pH to 7.0 with sodium hydroxideMobile Phase B Acetonitrile Gradient Time (min) % A % B 0.01 90.0 10.015.00 90.0 10.0 35.00 25.0 75.0 40.00 25.0 75.0 45.00 90.0 10.0 50.0090.0 10.0 Run Time 50.0 min Flow 1.0 mL/min UV Detector 210 nm(main)/254nm Injection Volume 5 μL Analysis Time 50.0 min Diluent Acetonitrile

Method C: method for monitoring the reaction of example 6 and 7 and thepurity of the compound of formula (I) wherein R₂ is hydrogen, via thefollowing GC method:

Column HP-5 30 m × 320 μm × 0.25 μm Front Inlet Heater 250° C. EntryPressure 7.3234 psi Total Flow 19.5 ml/min Septum Purge 3 ml/min CarrierGas Nitrogen Mode Split, Split Ratio: 10:1 Column Flow 1.5 ml/minInjection volume 0.2 ul Rate Value Hold Time Run Time Oven (° C./min) (°C./min) (° C./min) (° C./min)  60 0  0 10 300 5 29 Detection Flameionization Heater 300° C. H2 Flow rate 30 ml/min Air Flow rate 300ml/min Make up (N2) 25 ml/min

1. A process for the preparation of the compound of formula (III):

wherein R₁ is a C₁₋₄ linear or branched alkyl, comprising: a) reactingthe compound of formula (VI):

wherein R₁ is a C₁₋₄ linear or branched alkyl, with a compound offormula (VII):

wherein X₁ and X₂ are independently a halogen, mesilate, tosilate,besilate or triflate; for providing the compound of formula (V):

wherein R₁ is C₁₋₄ linear or branched alkyl; b) converting the compoundof formula (V):

obtained in step a) to give the compound of formula (III):

wherein R₂ is hydrogen, methyl or ethyl.
 2. The process according toclaim 1, wherein R₁ is ethyl.
 3. The process according to claim 1,wherein X₁ and X₂ are both bromine.
 4. The process according to claim 1,wherein the process in step a) is carried out by means of sodium hydrideor sodium hydride 60% in mineral oil.
 5. The process according to claim4, wherein the process is carried out in toluene.
 6. The processaccording to claim 1, wherein the process in step b) is carried out inn-butanol.
 7. The process according to claim 1, wherein the process instep b) is carried out in presence of acetic acid.
 8. The processaccording to claim 1, wherein the compound of formula (I), in which R₂is hydrogen, obtained at the end of step b), is purified bycrystallization or recrystallization from acetonitrile or a mixture ofacetonitrile and acetic acid.
 9. A compound chosen from the groupconsisting of: A compound of formula (II) or an optical isomer thereof,or salt thereof:

wherein R₂ is hydrogen, methyl or ethyl, and wherein R₁ is a C₁₋₄ linearor branched alkyl, with the exception of the compound of formula (II)wherein R₂ is hydrogen and R₁ is methyl; and a compound of formula (V):

wherein R₁ is a C₃₋₄ linear or branched alkyl.
 10. A compound accordingto the claim 9, having a formula selected from the group consisting of:

wherein R₁ is a C₁₋₄ linear or branched alkyl, with the exception of thecompound of formula (II-a) wherein R₂ is hydrogen and R₁ is methyl.